Hotter Plugs ..

Hi I've heard people mention puttin hotter plugs in the bike, just wondering what sort of effect this will have?

Not hotter plugs, but plugs that are happy to run at a higher temperature. I currently run CR9Es as I have the 4 degree ignition advance key fitted, and no problems so far.


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I need to put new plugs in and im going to be geting the igniton advance done at some point so would it be ok to run CR9Es on my current system, which is a K&N, 2nd 3rd mod and viper can?

When you say its happy to run at hotter temps does that mean its also happy to run at a normal temp?

There would be no problem running CR9Es on your current system, the only possible downside is that it could make cold starting a little more difficult, though in all honesty my bike starts perfectly with them in.

As you are unlikely to be running in ballistic mode during the winter you could also use the standard CR8Es I reckon and that was certainly my plan but I'm in two minds about it as the 9s are fine at minus two degrees.

It also runs at normal temps just fine .


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A short (hopefully simple) treatise on spark plugs * puts on Professor-type voice and glasses *

All spark plugs get hot inside the combustion chamber when the engine is running - because there is burning going on. That heat needs to be controlled; if the nose of the plug (the bit inside the engine) gets too hot at high speeds, then its temperature may ignite the fuel/air mix before the advent of the spark ("pre-ignition") with very nasty effects. If it doesn't get hot enough at low speeds, then it builds up carbon deposits which short the plug out ("fouling") and stops the engine from running.

The terms "hot" and "cold" are comparative and refer to the rate at which the nose dissipates that heat. Crudely, you need "hot" plugs for "cold" engines (ie ones with lower power, not just running temperature) and "cold" plugs for "hot" engines (ie ones with higher power).

BUT: Spark plugs are VERY carefully selected by the manufacturers of both plug and engine, and unless you have made changes to that engine, don't mess about - you don't need to. If you do, and get it wrong, you can wreck the engine. However, if you have tuned the engine in some way, eg increased the compression ratio, advanced the ignition timing** etc etc - then you may require a "colder" plug to dissipate the heat faster, and stop the plug from overheating.

It is always safe to go colder - the worst that happens is it fouls up at low speeds; it is VERY rarely safe to go hotter. Ideally what you should do is ask the people who have done the mods/provided the equipment what THEIR recommendations are. Or ring up the spark plug manufacturer and seek their advice.

(** There has been a previous thread on the effects of advance, with some really good comments from someone whose name I've forgotten.... )

I take my bike to the local dealership where I have had it serviced since 99 when I bought it, now 123k later, it still runs good, but sporadicly, uses oil at the beginning of fall, they told me they put in put in the plug that was 1 hotter than stock for better starts and high milage engine,

All I know is that it runs as good or better than it ever has since new(I've enjoyed the benefit of the free horsepower you get from frosty air the past few days )

I don't think changing heat range is necessary so long as your plug is burning the right color, if the plug color varies from optimal then you change heat range up or down accordingly

I know that my SV is a high milage engine that runs under rich conditions
when I had them install my V&H exaust, over 100k ago, they also installed the proper jetting to go with it.

and I don't know anything about whether you go hotter or colder or up or down numericly or what colors coinside with lean conditions or rich contitions, but I do know that my mechanic knows the relationship

With the latest very cold weather, I have found that the bike is a little harder to start with the CR9Es - immediately after firing it's very lumpy and not firing evenly, but this only last for a couple of seconds and then all is fine.


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Thats good to know I've just put in some CR9Es hoping to have the bike rebuilt today so i can fire her up

Only floor in this plan is with NGK (and other Jap plugs) the higher the number the Colder the plug

Copied from another site:-

The heat range numbers used by spark plug manufacturers are not universal, by that we mean, a 10 heat range in Champion is not the same as a 10 heat range in NGK nor the same in Autolite. Some manufacturers numbering systems are opposite the other, for domestic manufacturers (Champion, Autolite, Splitfire), the higher the number, the hotter the plug. For Japanese manufacturers (NGK, Denso), the higher the number, the colder the plug.

Yes but that's why I specified a CR9e, specific only to Champion .


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